3978 why is java so different... a session for cobol/pli/assembler developers

© 2015 IBM Corporation

© IBM Corporation 2011

Why are you so different?

Java for COBOL Developers

Tobias Leicher | CICS Client Technical Professional | [email protected]


IBM


IBMGoal of this Session

After running around and shouting „Java is just another language running on the mainframe“, it is now time to show you some lies about my fact.

Understand differences and reasons for them

See the advantages of different languages and also understand that there is no single language that rules the world

Get a feeling why problems in Java are different and a Dump in classical sense often leads you nowhere

Give Java another chance, that guy is now grown up and in his twenties, probably the time in life where you have enough experience to solve the important problems in life


IBMBefore we compare, let us rethink what we know already

Today we will talk about COBOL, PLI or even Assembler (LE) and we will compare it to Java, as I am a CICS Person I will talk more about CICS than IMS or Batch

So how does a COBOL Program executes in zOS (only cover LE here):

» The first thing that happens is a load of the program:○ In CICS the LOADER will issue a BLDL or LLACOPY MACRO against MVS and the Program is

loaded into the storage

» If you then Call the Program a new LE Enclave is----------------○ Wait, what is this LE guy used for again?!


IBMLE – The standardized Runtime Environment in zOS

Before LE all Languages brought their own Runtime Libraries

A Runtime library brings all the code that is provided by a language and not part of the user Program (Storage management, Math functions...)

A Runtime library has the advantage, that the code is always tied to the underlying hardware, without letting the compiler or the application do too much adaptions

Why now LE?

» When all the languages brought their own runtime, they expected to be alone in the world» Customers had problems to run different languages side by side

Back to our Topic!


IBMBefore we compare, let us rethink what we know already

Today we will talk about COBOL, PLI or even Assembler (LE) and we will compare it to Java, as I am a CICS Person I will talk more about CICS than IMS or Batch

So how does a COBOL Program execute in zOS (only cover LE here):

» The first thing that happens is a load of the program:○ In CICS the LOADER will issue a BLDL or LLACOPY MACRO against MVS and the Program is

loaded into the storage

» If you then Call the Program a new LE Enclave is initialized○ initial storage is obtained○ condition handlers initialized○ active member language specific run-time is initialized

» Control is given to the application code» Once the application ends and 'returns' to LE

○ The LE environment is terminated○ System resources obtained during initialization and throughout the execution of the application are

cleaned up


IBMHow does that look like?

= CICS Region

= CICS initial transaction

= Main Transaction Program or EC Linked Program


IBMSo what does the storage in LE look like?


IBM

CICS AS

How is a program dispatched then in CICS (abstracted)

zOSDispatcher

WEB

SWUQ

WEB WEB WEB

GlobalSRB

TCB

ASCB

CICS DFHSIP

TCBOTE

TCBOTE

LE Enclave LE Enclave

WEB

TCBQR

CICSDispatcher

LE Enclave LE EnclaveRTRQ


IBMSo in CICS a Task has one or more LE Enclaves that are totally seperated from each other Task in the address space

What happened with this great concept?!


IBMOnce upon a time...


IBMEveryone knew where to put their application, but suddenly things were different...


IBMSoon the workload starts spreading...


IBMEveryone was confused...


IBMAnd the new and shiny PC world was different to the Mainframe!

Less Users

Bad code has far more resources on its own

Coding Style Changed a lot

No LE, not even a unified Operating System (And Yes I know we have VM, VSE, TPF and Linux on the mainframe as well)

Backward Compatibility was not given anymore

...


IBMHistory of programming languages

1954 1959 1964 1971

SmallTalk

PL/I

COBOL

Fortran

1983

C

C++

LISP

Basic

1989

Perl

1995

OAK Java

JavaScript

© 2014 IBM Corporation17 March 6, 2015

IBMWhat is Java and what makes it different from what we have today

Java is What makes Java differentJava differes in some parts quite a lot from traditional languages like assembler, PL/I or COBOL Java is NOT compiled to executable code, it is

compiled to bytecode, that runs in a virtual machine The virtual machine uses the just-in-time compiler (JIT)

to execute the code Java is not based on programs, it is based on classes Java uses a garbage collector, that removes unused

objects from the storage Java development is often based on exiting

programming patterns (Design Patterns) Most of the build in funtionality of Java is based of

class libraries, that are build in the Java Runtime (JRE) Java contains a library for user interface development Java has the ability to reflect about the runtime with

several methods Java has a type safe variable declaration Uses JNI for native system calls and JDBC for

database calls

Java is an object oriented, platform independent, broadly supported and prevalent an state of the art language [and an Island in Indonesia]

Something YOU should care about

Java is not something new and not reliable an error-prone language the only solution for good code independent on it's own something that the distributed world should care of easy and/or out of the box a composable workbox full of libraries


IBMJava on Mainframes - what is different and why here?

IBM uses its own implementation of a JVM on mainframes that uses the underlying platform architecture

The Java workload can be offloaded to a zAAP processor

The Java logic can be a bridge between the mainframe and the distributed world

Java is a common language on many platforms that can help to find a dialog between the departments

Java is a language that is well known by many new professionals and so a good common ground, when they start to develop for mainframe applications

The language encourages a good design and loose coupling of components

IBM JDK for z/OS

Standard JSE(JDK specification)

zOS Extensions

Just In Time Compiler (JIT)Exploitation of the Hardware Architecture

z/OS Operating System and System z Hardware


IBMJava packaging and class hierarchies

Java modularity:

–Classes contain data and logic–Packages contain these classes and organize them

• This is just a virtual form of organization

–Jar files contain the classes and are the base for enterprise applications

Java visibility settings:

–Private, protected, package private, public

At the runtime, there are just a lot of classes on a classpath

jar file

java packages

class files

There are some features missing: jar visibility, versioning, dependencies


IBMThe Classpath – What was called a load lib concatenation before

Java VM

log4j

barcode4j

axis

batik

commons

derby

fop

ezmorph

freemarker

httpunit

jakarta

jcl

json

jdbm

jdom

jenks

jpos18

jython

looks

lucene

mail

mx4j

naming

jetty

poi

resolver

rome

serializer

servlets

tomcat

velocity

ws-commons

xalan

wsdl4j

xerces

xmlgraphics

xmlrpc

xmlapis

..

geronimo

bsh

bsf

guiapp

hhfacility

manufact.

marketing

minerva

accounting

assetmaint

base

bi

catalina

common

oagis

order

ebay

content

datafile

ecommerce

entity

googlebase

ofbiz

widget

minilang

party

pos.

product

workeffort

workflow

…

sunjce_prov.

plugin

jsse

jce

rt

dnsns

..

…

ClassNot

FoundException

BeginBeginHereHere


IBMSpecialty CP operation

Eligible work moves to specialty CP under control of z/OS Provide more capacity for eligible workloads without a change in MSU Provides more capacity for non-eligible workloads Reduces software stack charges for non-eligible products on CEC

Eligiblework

Eligiblework

Eligiblework

Eligiblework

Eligiblework

Eligiblework

GCP zIIPGCP


IBMIBM System z Application Assist Processor (zAAP)Dedicated to execution of Java workloads under z/OS® – e.g. Websphere®, CICS, IMS, DB2®

Available on all IBM zEnterprise systems, System z9 and z10 and zSeries z990 and z890

Used by any workload with Java cycles

Executes java code without any changes to the applications

Also used for XML parsing

Standard CP zAAP

WebSphere

Execute JAVA Code

z/OS Dispatcher

Suspend JVM task on z/OS standard logical processor

WebSphere

Java Application CodeExecuting on a zAAP

logical processorz/OS Dispatcher

JVM Switch to zAAP

JVMJVMSwitch to

z/OS Dispatcher

JVM

Dispatch JVM task on z/OS standard logical processor

JVM

z/OS Dispatcher

logical processor

z/OS Dispatcher

Dispatch JVM task on z/OS zAAP logical processor

JVMSwitch to standard processor

z/OS Dispatcher

Suspend JVM task on z/OS standard logical processor


IBMSo now let us see what happens in Java

Everything in Java is executed within a virtual machine

Run Time Data Management is done by the virtual machine

The JVM will only stop if the last non-deamon thread finishes

Java is never compiled upfront, it is interpreted and compiled during runtime

» Do you remember HPJ?

Java is platform independent, so everything in Java is abstracted (including Datatypes


IBMLets dive a bit deeper

Source: http://www.artima.com/insidejvm/ed2/jvmP.html


IBMHow does a Java LE-Enclave look like

C main procedure (JVM)

LE ThreadNativeStack

LE Heap Storage

Java Heap

Java Stack Classes

JIT Data


IBMIf we have a look at the LE Config for Java in CICS (DFHAXRO)

The LE Enclave is configured to always obtain new Heap Storage

» Bare in Mind that the JVM Heap Size is managed by the JVM, so a JVM can run out of memory

» initial 64-bit heap of 100MB » initial 31-bit heap of 4MB» Both areas allow incremental expansion to increase

The Files generated by the JVM are controlled by:

» DC C'ENVAR("_EDC_UMASK_DFLT=nnn")'

The output that is produced by the RPTO and RPTS options is written to the CESE transient data queue


IBM

CICS AS

So how is Java now executed in CICS (abstracted)

zOSDispatcher

WEB

SWUQ

WEB WEB WEB

GlobalSRB

TCB

ASCB

CICS DFHSIP

TCBOTE

TCBOTE

Java LE Enclave

JVM Thread

WEB

TCBQR

CICSDispatcher

LE Enclave LE EnclaveRTRQ

JVM Thread

JVM Thread

pThread

pThread


IBMWhat happens when a class got loaded


IBMWhat happens in the different phases

Loading: A class is obtained from a file and loaded to the JVM memory. Verifying: Check whether or not the read class is configured as described in the

Java Language Specification and JVM specifications. This is the most complicated test process of the class load processes, and takes the longest time. Most cases of the JVM TCK test cases are to test whether or not a verification error occurs by loading wrong classes.

Preparing: Prepare a data structure that assigns the memory required by classes and indicates the fields, methods, and interfaces defined in the class.

Resolving: Change all symbolic references in the constant pool of the class to direct references.

Initializing: Initialize the class variables to proper values. Execute the static initializers and initialize the static fields to the configured values.


IBMSo what happens higher above in the Compiler

The Java Bytecode for the following method:

Compiles to (javap -c):

public int sum(int a, int b) {int result = 0;result = a + b;return result;

}

public int sum(int, int); Code: 0: iconst_0 1: istore_3 2: iload_1 3: iload_2 4: iadd 5: istore_3 6: iload_3 7: ireturn


IBMSome more details (javap -v):

public int sum(int, int); flags: ACC_PUBLIC Code: stack=2, locals=4, args_size=3 0: iconst_0 1: istore_3 2: iload_1 3: iload_2 4: iadd 5: istore_3 6: iload_3 7: ireturn LineNumberTable: line 12: 0 line 13: 2 line 14: 6 LocalVariableTable: Start Length Slot Name Signature 0 8 0 this Lorg/leicher/java/samples/HelloWorldSum; 0 8 1 a I 0 8 2 b I 2 6 3 result I


IBMWhat happens now with this bytecode?

The JVM constructs for each Thread an execution engine In this engine the application now needs to be executed

» Problem?○ The JVM interpreting bytecodes can’t match the performance of native applications with machine

code○ Need to improve the performance of JVM startup (interpreting/compiling) and Java applications

over the life of JVM

» Solution!○ A compiler that will allow JVM to start reasonably quickly○ JIT code optimization processes○ Improve overall Java applications performance

The JIT Frontend is common in all IBM JVM Implementations, the Backend is specific to system z


IBMA Glance at JIT and the Interpreter

Java Application

JVM

JITCompiler

J9Interpreter


IBMThe Memory Management of the JVM

Heap Method Area Native Area

Young Generation Old Generation

Virt

ual

Fro

m

Sur

vivo

r 0

To

Sur

vivo

r 1

Ede

n

Tenu

red

Virt

ual

Permanent Generation

Runtime Constant Pool

Field & Method Data

Code

Virt

ual

Code Cache

Nat

ive

Com

pile

Threads (1..N)

Virt

ual

PC

Sta

ck NativeStack

-Xmx

Nr

GC

Eve

nts


IBMSo where are now the data of an Object

Heap

● Object HelloWorld● Object SimpleDateFormat● Object String● Object LOGGER

Method Area

● Class SimpleDateFormat● …

● Class Logger● …

● Class HelloWorld● Method: sayHello()● ...

Native Area

● Parameter reference:“message” to Stringobject

● Variable references● “formatter”● “today”

© 2014 IBM Corporation37

IBMCompare Cobol to Java

Develop a COBOL program

Cobol does not know complex DataTypes or Objects Data Elements are usually shared, not hidden The compile is usually done after coding (no online

syntax checking) Compiler perform less static tests Debugging is done in Multiuser Environments

Runtime Behaviour of Cobol

LE does not check wether the loaded program is corrupt

The runtime can not check whether the data is assigned correctly and Problems can arise

Handlers get control if something went wrong Memory is defined upfront

Develop a Java program

Data is structured in complex Objects Variables are not shared, they are adressed by

methods of the object Compiles are executed everytime a class is saved

(while ongoing syntax check is performed) Compiler performs a lot of static testing Debugging is usually done locally Memory can NEVER be addressed directly

Runtime Behaviour of Java

The JVM checks the bytecode after loading the class Classes are checked during compilation and in

Runtime data is only assigned if types match Classes and methods can throw exceptions (also JNI)

if a problem occurs New Objects can be generated very dynamical


IBMUpdate Behavior – “Java, why can't I just phase you in?”

Update a COBOL Program in CICS

COBOL Program is compiled/linked into a PDSe that is concatinated into the RPL upfront the existing Load Library or replace the existing version

In CICS issue a NEWCOPY or PHASEIN to let CICS reload the Program from the Dataset

Use the new Program

Update a Java Program in CICS

In Java you can't replace runtime code (except via JDWP)

Frameworks like OSGi enables the exchange of bundles

You need to decouple the application desing (using micro Services in OSGi or accept a small outage

Problems with this Approach

Compatibility is a contract that is not checked until runtime

The connection is something the compiler is not aware of

Problems with this Approach

The simple Phasein/Newcopy is not possible A complex Build infrastructure is necessary Only bundles/services, not classes can be “phased in” A change in Application Development Architecture is

necessary


IBMQuestions

Tobias Leicher

Client Technical Professional & zChampion

– CICS & CICS Tools

IBM Allee 1D-71139 Ehningen

Mobil: 0151 – 15 16 24 89Mail: [email protected]

Foto

VIELEN DANK FÜR IHRE AUFMERKSAMKEIT.

What’s next…

More of my sessions

#ASZ-3983: CICS Java Real-Life Projects, Featuring Datev

#ASZ-3978: Why Is Java So Different?: A Session for Cobol/PLI/Assembler Developers

#ASZ-5927: Meet the Experts of Generation z—Driving Innovation on the Mainframe

More Cloud sessions

#ASZ-2829: Liberté, Égalité, Fraternité—Viva the CICS and WebSphere Mini Revolution

#ASZ-6481: Java and CICS—A Perfect Match

#ASZ-1841: WebSphere Liberty Profile Support for Java Batch and the JSR-352 Specification, Featuring Sicoob

Collect a z Passport sticker here, and at…

@IBM_CICS slideshare.net/IBM_CICSfacebook.com/IBMCICS ibm.com/cics

WIN!

Get a lightning start: Key InterConnect 2015 sessions

#2829 Mon 2:00-3:00 Liberté, Égalité, Fraternité—Viva the CICS and WebSphere Mini Revolution

#1670 Tue 3:30-4:30 IBM WebSphere Liberty z/OS Connect: A Technical Introduction

#4032 Wed 9:30-10:30 Meet the Winners of IBM’s Mainframe Mobile App Throwdown 2014

#6482 Thu 11:00-11:50 What is the Mainframe Mobile App Throwdown and How Do I Register?

Register now at

ibm.biz/mmathrowdownand submit your app by April 12th

Mobilize your mainframe in our fun app-building contest forz Systems clients & business partners!

The Mainframe Mobile App Throwdownis back for 2015!

http://ibm.biz/mmathrowdown

http://ibm.biz/mmathrowdown

Need expert help?

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3978 why is java so different... a session for cobol/pli/assembler developers

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